The present invention relates to improved strip conductors for winding into coils and the coils made thereby. The coils may be used in transformers or other electrical gear. For the sake of simplicity, the invention will be described herein with reference to winding transformers, but it is to be understood that the invention has a scope wide enough to contemplate coils having various uses.
Transformer winding has been carried out for a great many years. In a transformer, typically two coils are formed and configured so that, when an alternating electric current is conducted through one, a magnetic field is set up which passes through the other, thereby inducing a current in the other coil. Depending upon the numbers of windings involved, the transformer may step up or step down the voltage of the primary coil to the voltage of the secondary coil. Transformers are widely used in electrical power distribution systems to increase their efficiency. As such, they handle high voltages and/or high currents. In order to handle the high currents involved, it has been found that providing the conductor to be wound into the coil in a sheet form is quite advantageous.
The conventional process for winding conductor sheets into a transformer is disclosed in a publication entitled "Concentration", Vol. 1, 1970 by Delbert W. Shobe of RTE Corp., 1900 E. North St., Waukesha, Wis. The transformers are wound from elongated sheets of bare aluminum (or in some cases copper) with interleaved layers of an insulating paper. The paper provides electrical insulation between layers (called "turns") of the wound conductor. An adhesive epoxy is applied to the paper in a diamond pattern before it is wound into the transformer. The completely wound transformer is heated to a high temperature to volatilize any liquids and, at the same time, the epoxy adhesive on the paper binds the conductor turns and paper turns together into a solid unit. After the conductor cools, it is loaded into a casing which is then filled with an insulating transformer oil, which penetrates the paper and the interstices between the diamond pattern of the epoxy adhesive. Connections to the two ends of the coil are typically made at the appropriate time in the processing by cold welding input and output terminations.
This general technique has been used for 20 or more years with adequate success. However, the volumes taken up by the transformer, including the paper, oil and adhesive, can become excessive, particularly when a great many turns are required in the fabrication of a transformer. The paper is typically 5 mils thick, so that 1000 turns would add considerably to the size and bulk of the transformer. The large size causes attendant large costs including a larger housing for the transformer, more oil required, greater shipping costs, and greater difficulties in installing the transformer.
Accordingly, there is a need in the art for a means and method to reduce the size and weight of the wound transformers.